Synthesis and In Vitro Antimicrobial Evaluation of New 1,3,4-Oxadiazoles Bearing 5-Chloro-2-methoxyphenyl Moiety

A series of new 1,3,4-oxadiazole derivatives, 4(a–h), containing 5-chloro-2-methoxy benzohydrazide moiety were synthesized by the reaction of 5-chloro-2-methoxybenzoate with different aromatic carboxylic acids. These newly synthesized compounds were characterized by FT-IR, 1H NMR, mass spectra, and also by elemental analysis. All the newly synthesized compounds were screened for their antibacterial and antifungal activities. Antimicrobial studies revealed that compounds 4c, 4f, and 4g showed significant activity against tested strains. 1. Introduction Resistance to number of antimicrobial agents among a variety of clinically significant bacteria is becoming increasingly important. There are various problems arising with the use of antimicrobials such as local tissue irritation, interference with wound healing process, hypersensitivity reactions, system toxicity, narrow antimicrobial spectrum, and emergency of resistance [1]. So, the increasing clinical importance of drug resistant microbial pathogens has additional urgency in microbiological and antifungal research. A wide variety of heterocyclic systems have been explored for developing pharmaceutically important molecules. Among them the derivatives of oxadiazoles have been playing an important role in the medicinal chemistry [2]. The 1,3,4-oxadiazole derivatives have been found to exhibit diverse biological activities such as antimicrobial [3, 4], anti HIV [5], antitubercular [6], antimalarial [7], anti-inflammatory [8, 9], anticonvulsant [10], and antitumor [11]. The 2,5-disubstituted-1,3,4-oxadiazole derivatives are known for various pharmacological activities such as antibacterial [12], antihypertensive [13], anticonvulsant [14], and antiproliferative [15]. The choice of 1,3,4-oxadiazole is due to its multiapplicability in the field of medicine. In the present study, some new 1,3,4-oxadiazoles 4(a–h) have been synthesized and characterized by different spectral studies. All the new compounds were screened for their antibacterial and antifungal studies. 2. Results and Discussion 2.1. Chemistry The novel 1,3,4-oxadiazoles 4(a–h) were synthesized according to Scheme 1. Formation of 1,3,4-oxadiazole derivatives, 4(a–h), was confirmed by recording their elemental analyses, FT-IR, 1H NMR, and mass spectra. The absorptions around 3050？cm？1 in synthesized compounds confirm the aromatic C–H stretching vibrations and the appearance of a medium to strong absorption bands above 1600？cm？1 due to a stretching vibration of the azomethine (C=N) bond formation in synthesized compound. The 1H NMR spectra of 4c